Pressure relief device assemblies

ABSTRACT

The present invention is directed to pressure relief devices and to corresponding pressure relief assemblies that have improved vacuum resistance, improved fragmentation resistance, and/or improved burst control while maintaining low mass. The pressure relief device includes a substantially flat flange section and a domed section. The domed section may include a transitional line that defines a change in the shape of the domed section. The pressure relief device may also include a bracket for securing or aligning a domed section to a flange section. The pressure relief device may further include a stress distribution feature that is disposed transversely to a line of weakness in the domed section. The pressure relief assembly may include a fastener having a wire that is configured to break and release the pressure relief device when subject to a predetermined tensile load.

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application no.60/259,691, filed on Jan. 5, 2001, which is expressly incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to pressure relief devices, assemblies, andcomponents, as well as methods of forming the same.

2. Background of the Invention

Many types of pressure relief devices exist in the art. These pressurerelief devices may include, for example, explosion panels, rupturedisks, vacuum supports, and valves. An explosion panel is one type ofpressure relief device that is typically used to provide emergencypressure relief under deflagration conditions in an environment such as,for example, a silo or a dust collector. An explosion panel may besubject to both a positive pressure differential and a negative pressuredifferential. In a positive pressure differential, the pressure withinthe environment is greater than the external pressure. In a negativepressure differential, the external pressure is greater than thepressure within the environment. In most circumstances, it is desirablefor the explosion panel to open when exposed to a predetermined positivepressure differential and to withstand a negative pressure differential.

Various efforts have been made to improve the vacuum resistance ofexplosion panels. For example, the explosion panel may be shaped toprovide a greater resistance to a negative pressure differential than apositive pressure differential. This may be accomplished by forming theexplosion panel with a domed shape and exposing the concave surface tothe pressure within the environment. This configuration provides greaterstructural integrity under negative pressure differentials than underpositive pressure differentials. Thus, the explosion panel may beconfigured to open when subject to a predetermined positive pressuredifferential yet be able to withstand a greater negative pressuredifferential.

In another method of improving vacuum resistance, a separate “vacuumsupport” may be included with the explosion panel assembly. This vacuumsupport may be attached to the concave side of the explosion panel toimprove the vacuum resistance. However, an explosion panel should openquickly and completely in response to the predetermined positivepressure differential. In many cases, the additional weight of a vacuumsupport will inhibit the ability of the explosion panel to quickly andcompletely open. In addition, the inclusion of a vacuum support mayincrease the costs associated with manufacturing the explosion panel.

To minimize explosion panel mass, designs that do not require a vacuumsupport are desirable. Higher mass vents will be less responsive to adynamic pressure rise. International Standards may limit the masspermitted; NFPA 68 has a mass limit of 2½ pounds per square foot.Alternatively, standards may require that ‘vent efficiency’ beexperimentally determined resulting in a greater vent area beingrequired for designs that are lower in efficiency. Higher mass typicallyresults in slower vent efficiency.

Various methods may be used to control the predetermined positivepressure differential at which the explosion panel will open. Forexample, a-series of slits may be cut into the explosion panel to definea series of “tabs.” The slits may be cut into the domed section of theexplosion panel or the flange section of the explosion panel. These tabsare configured to tail in tension when the explosion panel experiencesthe predetermined positive pressure differential. The number and size ofthe tabs will control the pressure differential at which the explosionpanel will open. Accordingly, the slits must be carefully cut to ensurethat the resulting tab has the appropriate size.

These slits may, however, reduce the vacuum resistance of the explosionpanel. When the slits are cut into the explosion panel, the structuralintegrity of the explosion panel is weakened. Thus, the explosion panelmay fail in the area of the slits when exposed to a negative pressuredifferential. Even if the explosion panel is exposed to a negativepressure differential that does not cause the panel to fail, repeatedpressure cycles may fatigue the tabs and thereby alter the pressuredifferential at which the explosion panel will open.

The pressure differential at which the explosion panel will open mayalso be controlled by securing the explosion panel to the environmentwith plastic bolts. The plastic bolts are configured to break when theexplosion panel is subject to the predetermined pressure differential.However, the operating conditions of the plastic bolts have a directimpact on the material strength of the bolt. Varying climate conditionsmay alter the material strength of the plastic bolts and, thus, thepressure differential at which the explosion panel will open. A plasticbolt may also fail at a much higher load under dynamic deflagrationventing conditions making prediction of behavior unreliable.

When a pressure relief device, such as, for example, a rupture disk, anexplosion panel, or a vacuum support, is exposed to the predeterminedpressure differential, a portion of the pressure relief device willtypically tear to create an opening. Safety considerations dictate thatthe opening material should remain attached to the nest of the pressurerelief device, instead of fragmenting. To prevent fragmentation, thepressure relief devices typically include an unweakened hinge area. Whenthe pressure relief device opens, the unweakened hinge area preventsfragmentation of the pressure relief device. However, when the pressurerelief device experiences a pressure differential that is significantlygreater than the predetermined opening pressure differential or asustained turbulent flow, the hinge area has a tendency to tear, therebyallowing the pressure relief device to fragment.

There is a need in the industry for a pressure relief device that iscapable of withstanding vacuum pressure, has a low mass and thereforeimproved dynamic performance, that will release at the predeterminedpressure regardless of the operating environment in which it is placed,that is resistant to operating pressure cycles, and opens withoutfragmentation. Different aspects of the present invention provide asolution to each of these identified problems.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to pressure reliefdevices, assemblies, and components that obviate one or more of thelimitations and disadvantages of prior art pressure relief systems. Theadvantages and purposes of the invention will be set forth in part inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Theadvantages and purposes of the invention will be realized and attainedby the elements and combinations particularly pointed out in theappended claims.

In accordance with one aspect, the present invention is directed to apressure relief device that includes a substantially flat flange sectionthat has a plurality of openings and that defines a plane. The pressurerelief device also includes adorned section that is connected to theflange section and has a transitional line that defines a change in theshape of the domed section. The transitional line is disposed outside ofthe plane defined by the flange section.

The present invention is further directed to a pressure relief devicethat includes a substantially flat flange section that has a pluralityof openings. Adorned section is joined with the flange section and has aconcave surface and convex surface. The domed section includes atransitional line that defines a change in the shape of the domedsection. A plurality of notches are disposed in the domed sectionadjacent the transitional line.

The present invention is still further directed to a pressure reliefdevice that includes a substantially flat flange section that has arectangular shape and a plurality of openings. A domed section is joinedwith the flange section and has a transitional line extending along theperimeter of the domed section. The transitional line defines a changein the shape of the domed section and forms a circle in the domedsection.

The present invention is also directed to a pressure relief assemblythat includes a frame and a pressure relief device. The pressure reliefdevice includes a substantially flat flange section configured to engagethe frame. The flange section defines a plane and has a plurality ofopenings. A domed section is joined with the flange section and has atransitional line that defines a change in the shape of the domedsection. The transitional line is disposed outside of the plane definedby the flange section. A plurality of fasteners are disposable throughone of the plurality of openings in the flange to secure the pressurerelief device to the frame.

According to another aspect, the present invention is directed to apressure relief device that includes a first structure having asubstantially flat flange section and a projection extending from theflange section. The pressure relief device also includes a secondstructure having a domed shape and an outer edge. A bracket having abody portion is configured to be securely engaged with the projection ofthe first structure. The bracket further includes a support configuredto engage the outer edge of the second structure.

The present invention is also directed to a method of making a pressurerelief device. A pressure relief device having a substantially flatflange section and a domed section is formed. The pressure relief deviceis separated into a first structure having the flat flange and a secondstructure having at least a portion of the domed section. A brackethaving a support is secured to the first structure. The second structureis engaged with the support of the bracket.

According to yet another aspect, the present invention is directed to apressure relief device that includes a substantially flat flangesection. A domed section is connected to the substantially flat flangesection. A line of weakness is formed in the domed section. The line ofweakness extends around a portion of the dome and terminates in two endpoints. A stress distribution feature is disposed substantiallytransversely to the line of weakness at each of the two end points ofthe line of weakness.

According to still another aspect, the present invention is directed toa fastener for engaging a pressure relief device with a frame. Thefastener includes a body portion configured to engage the frame. A headportion has an opening that is configured, to receive the body portionand a contact surface that is configured to engage the pressure reliefdevice. A wire connects the body portion to the head portion. The wireis configured to break and release the head portion when a predeterminedforce is exerted on the head portion.

The present invention is further directed to a pressure relief assemblyhaving a frame. A pressure relief device having a flange configured toengage the frame is provided. The flange includes at least one opening.A fastener having a body portion and a head portion is provided. Thebody portion is fixably connected to the frame and has a centralopening. A head portion having an opening engageable with the bodyportion is provided to secure the pressure relief device to the frame. Awire connects the body portion to the head portion and is configured tobreak and release the head portion when the flange exerts apredetermined force on the head portion.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention will be realized and attained bymeans of the elements and combinations particularly pointed out in theappended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1 is a top plan view of a prior art explosion panel.

FIG. 2 is a top plan view of an explosion panel in accordance with anexemplary embodiment of the present invention.

FIG. 3 is a top plan view of an explosion panel in accordance with anexemplary embodiment of the present invention.

FIG. 4 is a top plan view of an explosion panel in accordance with anexemplary embodiment of the present invention.

FIG. 5 is a top plan view of a rupture disk in accordance with anexemplary embodiment of the present invention.

FIG. 6 a is a pictorial representation of an explosion panel inaccordance with an exemplary embodiment of the present invention.

FIG. 6 b is a top plan view of an explosion panel in accordance with anexemplary embodiment of the present invention.

FIG. 6 c is a cross-sectional view of the explosion panel of FIG. 6 btaken along line AA.

FIG. 7 is a pictorial representation of a forming mold used to make theexplosion panel of FIGS. 68-6 c.

FIGS. 8 a-8 i are top plan views of the corner sections of an explosionpanel in accordance with exemplary embodiments of the present invention.

FIG. 9 is a pictorial representation of an explosion panel in accordancewith another exemplary embodiment of to the present invention.

FIG. 10 a is a top plan view of the explosion panel of FIG. 9.

FIG. 10 b is a cross-sectional view taken along the line BB in FIG. 10a.

FIG. 10 c is a cross-sectional view taken along the line CC in FIG. 10a.

FIG. 11 is a pictorial representation of a forming mold used to make theexplosion panel of FIGS. 9 and 10 a-10 c.

FIGS. 12 a-12 e are top plan views of an explosion panel in accordancewith exemplary embodiments of the present invention.

FIG. 13 a is a top plan view of an explosion panel in accordance withanother exemplary embodiment of the present invention.

FIG. 13 b is a pictorial representation of the explosion panel of FIG.13 a.

FIG. 14 a is a top plan view of an explosion panel in accordance withanother exemplary embodiment of the present invention.

FIG. 14 b is a cross-sectional view taken along the line AA in FIG. 14a.

FIG. 15 a is a top plan view of an explosion panel in accordance withanother exemplary embodiment of the present invention.

FIG. 15 b is a cross-sectional view taken along the line AA in FIG. 15a.

FIG. 16 a is a top plan view of an explosion panel in accordance withanother exemplary embodiment of the present invention.

FIG. 16 b is a cross-sectional view taken along the line AA in FIG. 16a.

FIG. 17 a is a pictorial representation of a fastener in accordance withan exemplary embodiment of the present invention.

FIG. 17 b is a sectional view of a fastener in accordance with anotherexemplary embodiment of the present invention.

FIG. 18 a is a sectional view of a fastener in accordance with anotherexemplary embodiment of the present invention.

FIG. 18 b is a bottom view of a head portion of the fastener of FIG. 18a.

FIG. 18 c is a top view of a body portion of the fastener of FIG. 18 a.

FIG. 19 is a side view of a pair of fasteners securing the flange of anexplosion panel to a frame in accordance with the present invention.

FIG. 20 is a pictorial representation of a bracket in accordance with anexemplary embodiment of the present invention.

FIG. 21 a is a front view of the bracket of FIG. 20.

FIG. 21 b is a top view of the bracket of FIG. 20.

FIG. 21 c is a side view of the bracket of FIG. 20.

FIG. 22 is a cross-sectional view of a bracket installed on a pressurerelief device in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

One aspect of the present invention has application in all types ofpressure relief devices. Such devices include, but are not limited to,rupture disks, explosion panels, and vacuum supports. In this respect,the present invention is directed to a method of reducing the likelihoodof fragmentation in such a pressure relief device. This reducedfragmentation potential is achieved by increasing the area over whichthe opening stresses are applied when the pressure relief device isactivated.

An exemplary explosion panel is illustrated in FIG. 1 and is designatedgenerally by reference number 11. As shown, explosion panel 11 includesa flange 13 and a central section 15. Flange 13 may have a square shapeas illustrated in the exemplary embodiment of FIG. 1. Alternatively,flange 13 may be any other shape commonly used in an explosion panel,such as, for example, rectangular, triangular, trapezoidal, or circular.

Flange 13 may include a plurality of openings 17. Openings 17 may bespaced around flange 13. Each opening 17 may be configured to receive afastener, such as, for example a bolt. A plurality of fasteners may bedisposed in openings 17 to secure explosion panel to a structure, suchas, for example, a frame.

Explosion panel 11 may be secured to a structure so that central section15 is exposed to an enclosed environment that may potentially experiencean increased pressure condition. For example, explosion panel 11 may beengaged with a silo or a dust collector. Explosion panel 11 may beconfigured such that central section 15 will open to create a vent pathwhen the pressure within the enclosed environment exceeds the externalpressure by a predetermined limit.

As also shown in FIG. 1, a line of weakness 10 may be disposed onexplosion panel 11. Line of weakness 10 may extend along a portion ofthe perimeter of explosion panel 11 and terminate in two end points 12.Line of weakness 10 may be, for example, a slit or a score line. Line ofweakness 10 is configured such that explosion panel 11 will open, ortear in the case of a score line, along line of weakness 10 whenexplosion panel 11 is exposed to a predetermined pressure differential.In the example of a score line, for example, the width and depth of lineof weakness 10 may be altered to change the predetermined pressuredifferential at which explosion panel 11 will open. In the case of aslit, line of weakness 10 may be intermittent. The spacing of the slitinterval may be altered to control the predetermined differentialpressure at which the explosion panel will open.

As described in greater detail below, central section 15 of explosionpanel 11 may have a domed shape with concave surface and a convexsurface. Line of weakness 10 may be formed in either the concave surfaceor the convex surface or be a slit connecting both surfaces. It shouldalso be noted that line of weakness 10 may be in the flange section 13of explosion panel 11 or line of weakness 10 may be disposed betweenflange section 13 and central section 15.

Thus, when the pressure of the fluid within the environment exceeds theexternal pressure by the predetermined level, the resulting force onexplosion panel 11 will cause the material of the explosion panel toopen along line of weakness 10. The continued force of the fluid onexplosion panel 11 and the force created by fluid escaping through theopening in central section 15 may cause the explosion panel to continueto open beyond line of weakness 10 to thereby increase the site of theopening.

As shown in FIG. 1, line of weakness 10 does not typically extend alongthe entire perimeter of explosion panel 11. A section of explosion panel11, commonly referred to as the hinge, may be left without a line ofweakness. It is expected that the propagation of the vent opening willstop at end points 12 and the explosion panel material will bend alongthe hinge area. Each end point 12 may include a small hole configured todistribute the stresses of the opening panel to prevent the materialfrom further tearing at either end point 12. Thus, the hinge area mayprevent the explosion panel from fragmenting.

In certain circumstances, however, the opening of explosion panel 11 maybe violent enough to cause the material to tear between the two endpoints 12. This tear may allow central section 15 to fragment from theremainder of explosion panel 11. In other words, explosion panel 11 mayexperience certain conditions that will cause a portion of the explosionpanel to be released into the flow of escaping fluid. The release orfragmentation of any portion of explosion panel 11 may pose a potentialsafety hazard.

In accordance with the present invention, the explosion panel mayinclude a stress distribution feature. Stress distribution feature mayextend substantially transversely to the line of weakness at each of thetwo end points of the line of weakness. As used in the presentdisclosure, the term “transversely” is used in its broadest sense tomean laying across the path of the line of weakness at any angle.

As illustrated in FIG. 2, a stress distribution feature 14 is disposedtransversely to line of weakness 10 at each end point 12. Each stressdistribution feature 14 may be any feature configured to distributestress. For example, each stress distribution feature may be a slit, ascore line, or a raised ridge that protrudes from either the concave ofthe convex surface of explosion panel 11.

As shown in FIG. 2, stress distribution feature 14 may be slightlycurved and have a “smiley face” configuration. It should be noted,however, that stress distribution feature 14 may be linear, have one ormore linear segments, one or more curved segments, or a combination oflinear and curved segments. It is further noted that stress distributionfeature 14 may have various radii of curvature and/or may be oriented atvarious angles relative to line of weakness 10.

Stress distribution feature 14 may prevent the fragmentation ofexplosion panel 11. If the opening of explosion panel 11 is violentenough to cause a tear to propagate from one or both of endpoints 12,each tear will encounter one stress distribution feature 14. Stressdistribution feature 14 provides a line of weaker material disposed in adirection transverse to line of weakness 10 and the expected directionof material tearing. When the material tear reaches stress distributionfeature 14, it is expected that any continued tearing will follow thedirection of weaker material of stress distribution feature 14. Thus,any continued tearing of the material of explosion panel 11 will likelybe in a direction that is transverse to the direction of line ofweakness 10. In this manner, stress distribution feature may divert ordeflect the direction of material tearing. Thus, stress distributionfeature 14 may prevent the tear from propagating across the hinge area.By preventing the two tears from meeting or by preventing one tear frompropagating across the hinge area, stress distribution feature 14 mayprevent explosion panel 11 from fragmenting.

In addition, a small hole 19 may be disposed at either end of eachstress distribution feature 14. Each small hole 19 may prevent thematerial of the explosion fluid on explosion panel 11 causes thematerial of explosion panel 11 to tear along stress distribution feature14, the tear may eventually reach the ends of stress distributionfeature 14. Small hole 19 at each end of stress distribution feature 14will distribute the tearing stresses over the circumference of the smallhole. Thus, greater stresses will be required to continue the materialtearing past the small hole. If the stresses are not great enough tocontinue tearing the material, the tear will end at the hole, therebypreventing fragmentation of explosion panel 11.

The present invention contemplates that any number of stressdistribution features may be used in combination to achieve the desiredobjective of diverting stress 1 and reducing the likelihood offragmentation upon opening of the pressure relief device. In theexemplary embodiment of FIG. 3, a pair of stress distribution features14 are disposed at each end point 12 of line of weakness 10.

The present invention further contemplates that the concept of thestress distribution feature may be incorporated into other types ofpressure relief devices. For example, as illustrated in FIG. 4, arupture disk 20 may include one or more stress distribution features 24.As one skilled in the art will recognize, rupture disks often include ascore line 22 and a hinge area 23. As shown, stress distributionfeatures 24 may be disposed adjacent the endpoints of score line 22. Asdescribed in connection with the explosion panel above, each stressdistribution feature may divert or deflect the direction of tearing toprevent the fragmentation of rupture disk 20. Stress distributionfeature 24 and score line 22 may be either slits or scores, or acombination of slits and scores.

Comparative testing of pressure relief devices with and without thestress distribution features of the present invention illustrate thatthe stress distribution features of the present invention are morelikely to prevent fragmentation of the pressure relief device. Forcomparison purposes, a pressure relief device without a stressdistribution feature was burst at 4 psi and a similar pressure reliefdevice that included a stress distribution feature was burst at 25 psi.In spite of the increased pressure differential on the pressure reliefdevice that included the stress distribution feature, the remaininghinge area on the pressure relief device with the stress distributionfeature was greater than the remaining hinge area on the pressure reliefdevice without the stress distribution features. Thus, the stressdistribution feature successfully diverted the direction of materialtearing.

Thus, incorporating a stress distribution feature of the presentinvention into a pressure relief device may allow for a smaller hingearea lobe used. Because the stress distribution feature deflects anymaterial tearing, the distance between the endpoints of the line ofweakness may be reduced without increasing the likelihood offragmentation. Accordingly, the pressure relief device may open tocreate a larger vent path through which fluid may escape. The largervent path translates to a lower flow resistance factor, K_(R), and anenhanced fluid flow through the activated pressure relief device.

As illustrated in FIG. 5, the stress distribution features of thepresent invention may also be applied to pressure relief assemblycomponents, such as, for example, a vacuum support 30. As shown, vacuumsupport 30 includes a line of weakness 32, which may be, for example, ascore line, that terminates in two endpoints 33. A series of four stressdistribution features 38 are disposed at each of the two endpoints 33.In the illustrated exemplary embodiment, stress distribution features 38have an arcuate, or “smiley face” configuration.

As further shown in FIG. 5, each of the stress distribution features 38initiates at an imaginary line 36 that would connect the two end points33 of line of weakness 32 to form a complete circle. The presentinvention contemplates that the stress distribution features may bedisposed on either side of imaginary line 36 or may straddle imaginaryline 36. In addition, an additional stress distribution feature 39 mayinitiate at each endpoint 33 of line of weakness 32. As described above,stress distribution features 38 and 39 will divert or deflect anytearing motion of vacuum support 30 material to a direction transverseto the line of weakness. In this manner, stress distribution features 38and 39 may prevent vacuum support 38 from fragmenting and allow ashorter distance between end points 33 which provides enhanced openingof the vacuum support.

Another aspect of the present invention has particular application indomed pressure relief devices that have a flange with a square orrectangular shape. These pressure relief devices, and in particular, thecorners of these pressure relief devices, are typically susceptible tofailure when subject to a negative pressure differential.

In accordance with the present invention, a pressure relief deviceincludes a flange and a domed section. The domed section includes atransitional fine that defines a change in the shape of the domedsection. For the purposes of the present disclosure, the phrase “changein the shape of the domed section” includes any distinct modification inthe shape of the domed section. For example, when viewed from across-sectional perspective, a change in the shape of the domed sectionmay be a change from a linear section to a curved section, a change inthe radius of curvature of the domed section, a marked change in theslope of the domed section, or another similar shape change. Asdescribed in greater detail below, the domed section may include one ormore transitional lines that extend along a portion or the entirety ofthe domed section.

As illustrated in FIGS. 6 a-6 c, a pressure relief device 40 includes aflange section 42. Flange section 42 may have a rectangular or squareshape and define a plane 41. Flange section 42 may also include a seriesof openings 43 (referring to FIG. 6 b) that extend around flange section42 and allow pressure relief device 40 to be secured to a frame 54(referring to FIG. 6 c) or other suitable support structure.

As further illustrated in FIG. 6 c, pressure relief device 40 alsoincludes a domed section 46 that has a concave surface 50 and a convexsurface 52. Domed section 46 is joined with flange section 42. Pressurerelief device 40 may be secured to frame 54 such that a positivepressure differential exerts a force on central domed section 46 in thedirection indicated by arrow 47 and a negative pressure differentialexerts a force on central domed section 46 in the direction indicated byarrow 46.

Domed section 46 also includes at least one transitional line 45.Transitional line 45 denotes a change in the shape of domed section 46.In the exemplary embodiment illustrated in FIGS. 6 a-6 c, domed section46 includes a series of four transitional lines 45. Each transitionalline 45 aligns with a corner of the square shaped flange section 42.When viewed from a top-down perspective, as illustrated in FIG. 6 b,each transitional line 45 may be a chamfer (linear section) or a fillet(curved section).

Referring to FIG. 6 c, domed section 46 includes a transitional section44 between flange 42 and transitional line 45. Transitional section 44may be substantially linear and project at an angle α from plane 41 sothat transitional line 45 is disposed outside of plane 41 defined byflange 42. It is contemplated that transitional section 44 may projectat any angle α from plane 41, although angle α is preferably betweenabout 20° and 45°. Domed section 4.6 extends at a greater, or steeper,angle from transitional line 45 to the apex of the dome. It should benoted that transitional section 44 may also have a curved shape and maybe constructed to be at least partially below plane 41.

The inclusion of transitional line 45 in each corner of explosion panel40 improves the ability of the explosion panel to withstand a negativepressure differential (i.e. a force in the direction of arrow 48 in FIG.6 c). When a negative pressure differential is exerted on explosionpanel 40, the steeper section adorned section 46 transmits the resultingforce to the transitional line 45. Transitional section 44, whichsupports the upper portion of domed section 46, transmits the force toflange section 42 and to frame 54. Thus, transitional line 45 acts as a“bridge” that transmits the compressive force of a negative pressuredifferential to the supporting frame 54.

In addition, transitional line 45 may facilitate the opening ofexplosion panel 40. In certain configurations of explosion panel 40, theburst control tabs are located in flange section 42, which is surroundedby a frame on either side. Accordingly, for explosion panel 40 to open,domed section 46 must collapse to allow a part of flange section 42 towithdraw from between the frames. The shallower angle of transitionalsection 44 provides additional clearance between the steeper portion ofdomed section 46 and a frame that may be disposed on the outlet side ofthe explosion panel. The additional clearance provides additional spacefor the domed section to flex and allow flange section 42 to withdrawfrom between the supporting frames.

As also shown in FIG. 6 c, a tab 56 may extend from frame 54. Tab 56 maybe configured to engage domed section 46 at or near transitional line 45to provide additional support under negative pressure differentialconditions. It is contemplated that a series of tabs 56 may bepositioned around frame 54 or around domed section 46 to provide supportfor the upper portion of domed section 46 at a plurality of locationsalong transitional lines 45.

A mold 60 for forming an explosion panel 40 is illustrated in FIG. 7. Asshown, mold 60 includes a frame 60 that defines an internal cavity 68. Aseries of supports 64 are disposed around internal cavity 68.

To form the explosion panel, a sheet of metal may be placed across thetop of frame 60. Pressure may then be applied to the sheet of metal todeform the metal into internal cavity 68. The depth of internal-cavity68 may be adjusted to accommodate the crown height of the domed sectionof the explosion panel. As the metal deforms, the deforming metal ateach corner of frame 62 will engage an edge 86 of each support 64. Eachedge 66 will form a transitional line 45 in the domed section 46 ofexplosion panel 40 (referring to FIGS. 6 a-6 c).

It is contemplated that various configurations of mold 64 and, thus,various configurations of explosion panel 40 will be readily apparent toone skilled in the art as improving the vacuum resistance of theexplosion panel. For example, instead of having supports 64 disposed ateach corner in the mold, mold may include supports 64 disposed at aselected few of the mold corners. The resulting explosion panel wouldinclude transitional lines only at corresponding locations. In addition,the size and shape of each support 64 may be varied to change the shapeof the resulting transitional line or lines. For example, the radius ofcurvature of each support 64 may be varied. Further, the edge 66 of eachsupport 64 may form a substantially straight line. Thus, the resultingexplosion panel may have transitional lines of many differentconfigurations in each corner.

FIGS. 8 a-8 i illustrate several exemplary embodiments of transitionallines 45. As shown in FIG. 8 a, transitional line 45 may have a “U”shape. As shown in FIG. 8 b, transitional line 45 may include a seriesof interconnected linear segments. As shown in FIG. 8 c, transitionalline 45 may be a curved segment. As shown in FIG. 8 d, a pair oftransitional lines 45 may be disposed in domed section 46. As shown inFIG. 8 e, transitional line 45 may include a plurality of interconnectedlinear segments. As shown in FIG. 8 f, transitional line 45 may be acurved section having endpoints that substantially coincide with theborder between flange section 42 and domed section 46. As shown in FIG.8 g, transitional line 45 may be comprised of two interconnected linearsegments. As shown in FIG. 8 h, transitional line 45 may be a curvedsegment having a center of curvature opposite to the curved segmentillustrated in FIG. 8 c. As shown in FIG. 81 transitional line 45 may bea substantially straight segment.

The present invention contemplates that many additional variations inthe disclosed transitional line may provide increased support for theexplosion panel under a negative pressure differential situation and areconsidered within the scope of the present invention. For example, thesize of the curved segments be varied. In addition, the curved segmentsmay be either centered or not centered with respect to the corners ofthe flange section. It is further contemplated that multiple curvedsections may be placed in parallel to each other in or adjacent to thecorners. Similarly, substantially straight segments, or chamfers, may beapplied, singularly or in parallel, adjacent to the corners of theflange section.

Other forms of strength-enhancing features may include diagonallyoriented features that begin at the panel corners and extend towards theapex of the dome. These diagonal features may develop either a concaveor convex facing corner ridge in the explosion panel. It is contemplatedthat a diagonal ridge feature may intersect the transitional line andmay further increase the vacuum strength of the panel. Such ridges mayor may not be perpendicular to the transitional line.

The present invention contemplates any transitional line that enhancesvacuum support strength by applying a shape modification to the domeprofile. These transitional lines may be formed in the plane of theflange section or may be elevated with respect to that plane.Alternatively, the strengthening feature can be formed below the planeof the vent flange.

The present invention further contemplates that the transitional linemay extend around the entire perimeter of the explosion panel, insteadof being limited to one or more corners of the panel. For example, FIGS.9 and 10 a-10 c illustrates an explosion panel 40 that includes atransitional line 45 that extends around the perimeter of domed section46.

As shown in FIG. 10 a, explosion panel 40 has a square-shaped flangesection 42. Transitional line 45 includes a series of curved sections 70connected by a series of straight sections 72. Each of the straightsections 72 may be disposed at equal distances from flange section 42and each of the curved sections 70 may be disposed at equal distancesfrom the corners of flange section 42. However, the distance betweenflange section 42 and transitional line 45 will be greater along curvedsections 70 than along straight sections 72. Accordingly, as shown inFIGS. 10 b and 10 c the length of transitional section 44 will begreater in the corners (referring to FIG. 10 c) than in the straightsections (referring to FIG. 10 b).

FIG. 11 illustrates a mold 60 configured to form an explosion panel 40as illustrated in FIGS. 9 and 10 a-10 c. As shown, edge 66 of support 64extends along the entire perimeter of frame 62. Thus, when the sheet ofmetal is deformed into cavity 68, edge 66 will form a transitional line45 that extends around the perimeter of the domed section.

The extended transitional line will provide additional support for thedomed section of the explosion panel when exposed to a negative pressuredifferential. As described above, the compressive force resulting fromthe negative pressure differential will be directed through thetransitional line to the supporting frame. With the extendedtransitional line, the additional support will be provided around theentire explosion panel.

The present invention contemplates that many variations of the extendedtransitional area will be readily apparent to one skilled in the art.Several additional exemplary embodiments of explosion panels havingextended transitional lines are illustrated in FIGS. 12 a-12 e. Theexplosion panel illustrated in FIG. 12 a includes a rectangular flangesection 42 and a pair of semi-circular transitional lines 45 that opentowards each other. The explosion panel illustrated in FIG. 12 bincludes a rectangular flange section 42 and a circular transitionalline 45. The explosion panel illustrated in FIG. 12 c includes a squareflange section 42 and a circular transitional line 45. The explosionpanel illustrated in FIG. 12 d includes a square flange section 42 and ahexagonal transitional line 45. The explosion panel illustrated in FIG.12 b includes a rectangular flange section 42 and “FIG. 8” transitionalline 45. It is contemplated that many other variations on the extendedtransitional line may be readily apparent to one skilled in the art andare considered within the scope of the present invention.

As illustrated in FIGS. 13 a and 13 b, explosion panel 40 may be formedwith a series of ridges 76, or other reinforcing features. Ridges 76 mayprovide additional support against a force resulting from a negativepressure differential. In the illustrated embodiment, ridges 76 extendfrom transitional line 45 to each corner of flange section 42. It iscontemplated, however, that the explosion panel may include additionalreinforcing features around domed section 46.

The present invention further contemplates that the transitional linesmay extend from flange section 42 into domed section 46. As shown inFIGS. 14 a and 14 b, a series of three transitional lines 45 may extendfrom either side of rectangular flange section 42 into domes section 46.The transitional lines 45 may be parallel or, as illustrated in FIGS. 15a and 15 b, the transitional lines 45 may be disposed at angles relativeto each other. In addition, as illustrated in FIGS. 16 a and 16 b,explosion panel 40 may include three transitional lines 45 that extendfrom one side of flange section 42 and two transitional lines 45 thatextend from the opposite side of flange section 42. It is furthercontemplated that many other variations on this aspect may be readilyapparent to one skilled in the art and are considered within the scopeof the present invention. For example, an explosion panel may includeone or more transitional lines on one side of the domed section and zeroor more transitional lines on the opposite side of the domed section.

In accordance with another aspect of the present invention, a fasteneris provided to secure the flange section of the explosion panel to theframe. The fastener includes a head portion and a body portion. A wireconnects the head portion to the body portion and is configured to breakwhen exposed to a predetermined tensile load.

As illustrated in FIG. 17 a, a fastener 80 includes a head portion 62and a body portion 84. Head portion 82 includes a flange 87 having acontact surface 88. Head portion 82 also includes a first opening 89extending from contact surface 88. Head portion 82 further includes asecond opening 93 that extends from first opening 89 to the top of headportion 82.

In addition, head portion 82 may include a conventional hexagonal bolthead 96. Bolt head 96 may be engaged by a tool, such as, for example, awrench, to apply a torque to head portion 82. Bolt head 96 may be of anyconfiguration readily apparent to one skilled in the art.

As also illustrated in FIG. 17 a, body portion 84 includes a centralopening 87 that may extend through body portion 84. Body portion 84 isdisposable in first opening of head portion 82 so that central opening87 aligns with second opening 93 in head portion 82. Body portion 84 mayalso include a series of threads 86. Threads 86 may be configured tomate with corresponding threads in a frame or to mate with a nut.

As further shown in FIG. 17 a, a wire 90 is disposed through secondopening 93 in head portion 82 and through central opening 87 in bodyportion 84. A first locking member 92 is secured to wire 90 adjacenthead portion 82. A second locking member 94 is secured to wire 90adjacent body portion 84. First and second locking members 92 and 94 maybe secured to wire 90 after body portion 84 is disposed within firstopening 89 of head portion 82 to prevent body portion 84 fromdisengaging head portion 82.

Wire 90 is configured to fail when subject to a predetermined tensileforce. As one skilled in the art will recognize, various characteristicsof the wire may be altered to vary the force at which the wire willfail. For example, the wire gauge or material may be changed to vary thetensile strength of the wire. When the wire experiences a tensile loadthat equals or exceeds the tensile strength of the wire, the wire willfail and allow body portion 84 to disengage from head portion 82.

As shown in FIG. 19, a series of fasteners 80 (two of which areillustrated) may be used to secure flange section 42 of an explosionpanel to frame 54. Contact surface 88 of each head portion 82 engagesthe outlet surface of flange section 42. A gasket 55 may be disposedbetween flange section 42 and frame 54.

Fasteners 80 may be used to control the pressure differential at whichthe explosion panel opens. When the explosion panel experiences apositive pressure differential, flange section 42 will exert acorresponding force on each contact surface 88 of each fastener 80. Ifthe force exerted by flange section on each contact surface 88 exceedsthe tensile strength of wire 90, the wire will break and allow headportion 82 of each fastener 80 to disengage the respective body portion84. After each wire 90 in each fastener 80 breaks, flange section 42 isfree to move relative to frame 54 to open the explosion panel. It willbe readily apparent that the pressure differential at which theexplosion panel will open may be varied by modifying the wire withineach fastener or by adjusting the number of fasteners used to secure theexplosion panel to the frame.

Alternatively, as shown in FIG. 17 b, body portion 84 of a series offasteners 80 (one of which is illustrated) may be welded or otherwisesecurely fastened to frame 54, such as in a “stud bolt.” In thisconfiguration, flange section 42 of explosion panel is placed over thebody portions 84 and an outlet frame (not shown) and/or head portion 82are used to fix the explosion panel to the frame. Body portion 84 mayinclude a pin 99 that is placed in an opening 104 disposed transverselyto central opening 87. Wire 90 may be looped around pin 99, so thatfirst and second locking members 92 and 94 may be disposed adjacent headend 82 of fastener 80 to connect head portion 82 with body portion 84.Wire 90 will therefore hold flange section 42 against frame 54 until thepressure differential causes wire 90 to break.

In yet another embodiment, head portion 82 may include an opening 106that is configured to align with opening 104 in body portion 84. Wire 90may be disposed through openings 104 and 106. First and second lockingmembers 92 and 94 may be disposed on opposite sides of head portion 82so that wire 90 connects head portion 82 with body portion 84 offastener 80. Wire 90 will therefore hold flange section 42 against frame54 until the pressure differential causes wire 90 to break.

The present invention contemplates that fasteners 80 may be disposedaround the entire perimeter of flange section 42. Alternatively,fasteners 80 may be disposed around a portion of flange section 42 andconventional fasteners may be used to secure the remaining portions offlange section 42 to frame 54. In this embodiment, the conventionalfasteners may define a hinge area. The conventional fasteners will notbreak when the wires 90 of each fastener 80 break. Thus, at least aportion of the flange section will remain fixed to the frame. In thismanner, fragmentation of the explosion panel may be prevented.

As shown in FIG. 17 a, an activation pin 98 may be used to secure headportion 82 to body portion 84. Head portion 82 includes an opening 100that aligns with a corresponding opening 102 in body portion 84.Activation pin 98 may be disposed through openings 100 and 102 to securehead portion 82 to body portion 84 prior to the installation of fastener80. When a torque is applied to head portion 6240 secure the flangesection to the frame, activation pin 98 will prevent head portion 82from rotating relative to body portion 84. A rotation of head portion 82relative to body portion 84 may cause wire 90 to twist and therebyaltering the force at which the wire will fail. Once fastener 80 is inplace, activation pin 80 may be removed to “activate” the fastener.

Alternatively, as shown in FIGS. 18 a-18 c, first opening 89 of headportion 82 and body portion 84 may include mating surfaces that willtransmit a torque while still allowing head and body portion to easilydisengage when the wire 90 breaks. For example, first opening 89 mayhave a hexagonal shape. Body portion 84 may include a correspondinghexagonal projection 91. When hexagonal projection 91 is engaged withfirst opening 89, a torque applied to head portion 82 may be transmittedto threads 86 of body portion 84 without altering the tensile strengthof wire 90. It is contemplated that alternative configurations will bereadily apparent to one skilled in the art.

In accordance with the present invention, a bracket for joining twosections of a pressure relief device is provided. A pressure reliefdevice, such as an explosion panel, may be split into two structures, afirst structure having a substantially flat flange section and a secondstructure having a domed section with an outer edge. The bracket may besecured to the first structure. The bracket includes a supportconfigured to receive the outer edge of the second structure. Thebracket may be used to align the second structure relative to the firststructure or to connect the first structure with the second structureand control the set pressure of the explosion panel.

As illustrated in FIGS. 20 and 21 a-21 c, a bracket 110 includes a bodyportion 112 and a support 114. Support 114 may be disposed substantiallyperpendicular to body portion 112 or at an angle relative to bodyportion 112. A set of guides 122 may be disposed on either side ofsupport 114. In the exemplary illustrated embodiment, each guide 122includes a section that is angled away from support 114.

Bracket 110 may also include a tab 116. Tab 116 is disposed adjacentsupport 114. Tab 116 may include a pair of slits 118 that define afailure region 120. As described in greater detail below, slits 118 maybe configured such that failure region 120 will fail when subject to apredetermined tensile load.

As illustrated in FIG. 22, bracket 110 is configured to join a firststructure 124 and a second structure 128 to form a pressure reliefdevice. First structure 124 includes a substantially flat flange section125 that may include a series of openings (not shown). First structure124 may also include a projection 126 that extends from flange section125. Second structure 128 has a domed shape with an outer edge 129.First and second structures 124 and 128 may be created by cutting aformed explosion panel along the domed section. It is contemplated thata conventional explosion panel or an explosion panel according to anyaspect of the present invention may be cut along the domed section toform first and second structures 124 and 128.

As shown, body portion 112 may be secured to projection 126 through aprocess such as, for example, spot welding. Body portion 112 may extendalong the entire periphery of projection 126. Alternatively, a series ofbrackets 110 may be disposed along the periphery of projection 126.

When body portion 112 is secured to first structure 124, support 114 isconfigured to receive outer edge 129 of second structure. Support 114will provide support for the domed section of the explosion panel whenthe explosion panel is subject to a negative pressure differential. In aconventional explosion panel, which typically includes a circumferentialslit to control burst pressure, the forces associated with a negativepressure differential will cause the upper portion of the explosionpanel to override the lower portion of the explosion panel. In otherwords, an explosion panel having burst control tabs defined by a seriesof slits, or stitches, may be particularly susceptible to failure whensubject to a negative pressure differential. The bracket of the presentinvention prevents the upper portion of the explosion panel fromoverriding the lower portion of the explosion panel Thus, a pressurerelief device that includes a bracket may be less susceptible to failurewhen subject to a negative pressure differential.

Guides 122 are configured to ease the engagement of second structure 128with support 114. In this manner, bracket 110 may be used as analignment mechanism to join the domed section of the explosion panelwith the flange section.

Tab 116 may be secured to second structure 128 to provide burst controlin a positive pressure differential condition. When outer edge 129 ofsecond structure 128 is engaged with support 114, stab 116 is positionedadjacent the convex surface of second structure 128. Tab 116 may besecured to second structure 1.28 through a process such as, for example,spot welding. Alternatively, tab 116 may be secured to second structure128 by any other method readily apparent to one skilled in the art suchas, for example, a wire closure. When tab 116 is secured to secondstructure, the explosion panel will be able to resist the tensile forcesassociated with a positive pressure differential. The failure region 120of tab 116 may be configured to fail when the tensile force reaches apredetermined limit. In this manner, bracket 110 may be used to bothsupport the explosion panel under a negative pressure differential andto provide burst control when the explosion panel is subject to apositive pressure differential.

When using bracket 110 with an explosion panel as described above,a-series of notches 130 may be formed in the domed section. Notches 130may have a depth substantially equivalent to the thickness of support114. As shown in FIG. 9, domed section 46 of explosion panel 40 mayinclude a series of notches 130 that are disposed adjacent transitionalline 45. Each notch 130 is configured to receive one support 114. Bodyportion 112 of bracket 110 may be spot welded to transitional section 44when support is within notch 130. When bracket 110 is engaged with notch130, dome section 46 will rest on support 114 (referring to FIG. 20)and/or on projection 126. Thus, a compressive force resulting from anegative pressure differential will act on either support 114 ortransitional section 44. This will prevent tab 116, when attached todomed section 46, from experiencing cyclical pressure fluctuations thatmay fatigue tab 116 and thereby alter the material strength of failureregion 120. The same concept may be used without a transitional line 45by placing bracket 110 between an upper and lower dome area of a simpledomed structure separated by a slit.

The bracket of the present invention may reduce the costs associatedwith manufacturing an explosion panel that will open when exposed to acertain pressure differential. As will be recognized by one skilled inthe art, the configuration of burst control tabs necessary to achievethe desired opening characteristics is often determined through aniterative testing process. In other words, an operator may have torepeatedly test different burst control tab configurations to identifythe configuration necessary to allow the explosion panel to open whensubject to the predetermined pressure differential. In a conventionalexplosion panel, where the burst control tabs are formed directly in thedomed section, this may require that the operator repeatedly move asample explosion panel between a slit cutting device and a testingdevice to determine the proper configuration of the burst control tabs.This process may be expensive and time-consuming.

When using a bracket according to the present invention to control theburst pressure of the explosion panel, only the burst control tabs 116of the bracket will need to be reconfigured in the iterative testingprocedure. Thus, the burden of transporting the explosion panel betweenthe testing and cutting locations may be removed. In addition, the burstcontrol tabs of the bracket may be formed and reconfigured throughstamping process, which is less expensive than the cutting process.Moreover, in the testing process of the brackets, only the material ofthe bracket is subject to destruction, instead of the entire explosionpanel. Thus, the bracket of the present invention may reduce the costsassociated with manufacturing and testing an explosion panel.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the aforementionedembodiments without departing from the scope or spirit of the invention.Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1-63. (canceled)
 64. A pressure relief device, comprising; a firststructure having a substantially flat flange section; a second structurehaving a domed shape and an outer edge; and a bracket having a bodyportion configured to be securely engaged with the first structure and asupport configured to engage the outer edge of the second structure. 65.The pressure relief device of claim 64, wherein the bracket includes atleast one tab configured to be securely engaged with the secondstructure and further configured to withstand a predetermined tensileforce.
 66. The pressure relief device of claim 65, wherein the secondstructure includes a notch configured to receive the at least one tab.67. The pressure relief device of claim 65, wherein the second structureincludes a concave surface and a convex surface and the tab is securelyengaged with the convex surface.
 68. The pressure relief device of claim64, wherein the bracket extends along the entire perimeter of the firststructure.
 69. The pressure relief device of claim 65, wherein thebracket includes a plurality of tabs configured to be securely engagedwith the second structure.
 70. The pressure relief device of claim 64,wherein the support of the bracket includes a pair of guides.
 71. Thepressure relief device of claim 70, wherein the guides extend at anangle relative to the body portion.
 72. The pressure relief device ofclaim 64, wherein the support is substantially perpendicular to the bodyportion.
 73. The pressure relief device of claim 64, wherein the bodyportion of the support is spot welded to the first structure.
 74. Amethod of making a pressure relief device, comprising: forming apressure relief device having a substantially flat flange section and adomed section; separating the pressure relief device into a firststructure having the flat flange and a second structure having at leasta portion of the domed section; securing a bracket having a support tothe first structure; and engaging the second structure with the supportof the bracket.
 75. The method of claim 74, wherein the bracket is spotwelded to the first structure.
 76. The method of claim 74, furtherincluding the step of securing the second structure to the bracket. 77.A fastener for engaging a pressure relief device with a frame,comprising: a body portion configured to engage the frame; a headportion having an opening configured to receive the body portion and acontact surface configured to engage the pressure relief device; and awire connecting the body portion to the head portion, the wireconfigured to break and release the head portion when a predeterminedforce is exerted on the head portion.
 78. The fastener of claim 77,wherein the head portion includes a flange having the contact surface.79. The fastener of claim 77, wherein the body portion includes threads.80. The fastener of claim 77, wherein each of the body portion and headportion include a central opening and the wire is disposed within thecentral opening of both the body portion and the head portion.
 81. Thefastener of claim 80, wherein a first locking member is securely fixedto a first end of the wire and is configured to engage the head portionand a second locking member is securely fixed to the second end of thewire and is configured to engage the body portion.
 82. The fastener ofclaim 77, further including a pin selectively engageable with the bodyportion and the head portion to secure the body portion to the headportion.
 83. The fastener of claim 82, wherein each of the body portionand head portion includes a pin opening configured to receive the pin.84. The fastener of claim 77, wherein the opening in the head portionhas a hexagonal shape configured to receive a corresponding hexagonalprotrusion on the body portion.
 85. A pressure relief assembly,comprising: a pressure relief device having a flange including at leastone opening; and a fastener having: a body portion fixably connected tothe frame and having a central opening; a head portion having an openingengageable with the body portion to secure the pressure relief deviceduring use; and a wire connecting the body portion to the head portion,the wire configured to break and release the head portion when theflange exerts a predetermined force on the head portion.
 86. Thepressure relief assembly of claim 85, wherein a pin is disposedtransversely to the central opening of the body portion and the wireloops around the pin.
 87. The pressure relief assembly of claim 86,wherein a pair of locking members are secured to each end of the wire.88. The pressure relief assembly of claim 85, wherein a plurality offasteners are disposed around a perimeter of the pressure relief device.89. The pressure relief assembly of claim 85, further including a gasketdisposed adjacent the flange of the pressure relief device.
 90. Thepressure relief assembly of claim 85, wherein the pressure relief deviceis an explosion panel.
 91. The pressure relief assembly of claim 85,wherein the body portion includes an opening and the head portionincludes an opening configured to align with the opening in the bodyportion, the wire disposable through the opening in the head portion andthe opening in the body portion to secure the head portion to the bodyportion.
 92. The pressure relief assembly of claim 85, wherein the bodyportion includes threads.
 93. The pressure relief device of claim 64,wherein the first structure includes a projection extending from theflange section and the body portion of the bracket is configured to besecurely engaged with the projection of the first structure.
 94. Thepressure relief device of claim 65, wherein the second structureincludes a concave surface and a convex surface and the tab is securelyengaged with the concave surface.